fix(content): keep the stored title in the sidebar after a create

[DavidBabinec]

The bug

Creating a post while the entries list was still loading left a nameless row in the Content sidebar. The entry saved correctly and the editor showed its "Untitled" placeholder, but the sidebar row rendered with only an author and a status. The same click worked most of the time, because which request finished first decided the outcome.

The fix

createUntitledEntry stores "Untitled" on the server but hands the editor a copy whose title is blank, so the title field shows its placeholder. loadEntries merged that editor copy back into the list whenever an in-flight load resolved after the create. The workspace now keeps the stored row alongside the editor view and rebuilds the list from the stored one. An MCP save, where the selection genuinely is the newer row, still merges as before.

Verification

bun test                                    # 6618 pass, 0 fail (3 runs)
bun run build                               # clean
bun run lint                                # clean
bunx playwright test content-create-race    # CONTENT-009 passed

The Playwright line reports 6 passed because the e2e project pulls in auth setup, dashboard preflight, and personas first. CONTENT-009 is the only test covering this fix.

New coverage at unit and browser level. Both hold the list response until the create lands, and both fail without the fix.